Compressor plants, for example natural gas compressor plants, for gas transport and/or gas storage are important devices in the sense of the national and international energy supply. A system for gas transport comprises a large number of compressor loans, which in each case can be composed of a plurality of compressor units. Here, the compressor units are given the task of adding sufficient mechanical energy to a conveyed medium in order to compensate for friction losses and to ensure the necessary operating pressures and flows. Compressor units often have very different drives and impellers, since they are for example designed for base load or peak load operation. A compressor unit comprises, for example, at least one drive and at least one compressor.
The automation of plant is given great significance, in particular for operation with optimal costs. The capability of the plant automation system to manage the process and to optimize the compressor plant within the production restraints supplies decisive economic advantages.
The compressors of a compressor plant are frequently driven by turbines which cover their fuel requirements directly from a pipeline. Alternatively, compressors are driven by electric motors. Operation with optimal costs means minimizing the power consumption of the turbines or the electric drives at a given compressor output, delivery output, delivery capacity and/or with a given volume flow.
A usable operating range of compressors is restricted by disadvantageous effects of internal flow processes. This results in operating limits, such as a temperature limit, exceeding the local speed of sound (compressor surge, absorption limit), the circumferential breakdown of the flow at the impeller or the pump limit.
The automation of a compressor plant primarily has the task of implementing set points predefined by a central dispatching facility, such as optionally a flow through the station or final pressure at the output side, as actual values. In this case, predefined limiting values for the intake pressures on the inlet side, the final pressures on the outlet side and the final temperature at the outlet from the plant must not be exceeded.
WO 03/036096 A1 discloses a method for optimizing the operation of a plurality of compressor units of a natural gas compression station. In this method, after a second or a further compressor unit has been started up, the rotational speeds of the running compressor units are run in a fixed rotational speed relationship in relation to characteristic map data for each compressor unit. In order to implement a first reduction in the energy consumption, after an additional compressor has been started up, the rotational speeds of all the units that are operating are changed by an equal-percentage flow rate adjustment until, if possible, all the pump protection valves in the plant are closed. Only after the all pump protection valves have been closed are working points of the compressor units in their characteristic maps displaced as close as possible to a line of maximum efficiency.
According to EP 0 769 624 B1, a method is known for load compensation between a plurality of compressors and for manipulating the working output of the compressors in order to maintain a predetermined relationship between all the compressors if the working points of all the compressors are further from the pump limit than a specified value.
EP 0 576 238 B1 discloses a method and a device for load distribution. Using a compressor intended as a reference compressor, a control signal is generated which is used as a reference variable for the non-reference compressors.